This invention is related to lubricating oils, and more particularly to an ashless, antioxidant lubricating oil additive.
In developing lubricating oils there have been many attempts of providing additives which impart antioxidant properties in the lubricating oils. Zinc dithiophosphates have been used in formulated motor oils as antioxidant additives for more than fifty years. However, zinc dithiophosphates give rise to ash which contributes to particulate matter found in automotive exhaust emissions. It is important to limit the particulate matter formed during engine use for toxicological and environmental reasons, but it is equally important to maintain undiminished antioxidant properties of the lubricating oil.
Thus, it is an object of this invention to provide an ashless, antioxidant additive which imparts these desired properties to a lubricant.